With traditional extrusion a billet of material is pushed and/or drawn through a die to create a rod, rail, pipe, etc. Various applications leverage this capability. For instance, extrusion can be used with food processing applications to create pasta, cereal, snacks, etc., pipe pastry filling (e.g., meringue), pattern cookie dough on a cookie pan, generate pastry flowers and borders on cakes, etc. In another application, extrusion can be used with consumer goods, for example, to merge different colored toothpastes together on a toothbrush.
FIG. 11 is a perspective view showing an extrusion head 30 of a conventional micro extrusion system for producing fine featured (e.g., less than 50 micron width and height) structures 20 on the upper surface 102 of a substrate 101. Extrusion head 30 that includes metal plates 31, 32 and 33 that are laminated together using known high pressure wafer bonding techniques, with one or more of the plates being processed to define a fluidic channel 34 that communicates with an outlet orifice 35 that is defined on a side edge of the head. Extrusion material is inserted into fluidic channels 34 through an input port 37 such that the extrusion materials are shaped and extruded through outlet orifice 35, from which they are dispensed onto a target structure (e.g., upper surface 102 of substrate 101).
FIGS. 12(A) and 12(B) are cross sectional side views illustrating a typical production problem associated with conventional micro extrusion systems. FIG. 12(A) shows an idealized high aspect-ratio extruded structure 20A formed on substrate 101 using the conventional micro extrusion techniques described above, with idealized extruded structure 20A having the square or rectangular shape of outlet orifice 35. For purposes of explanation, idealized extruded structure 20A that has a relatively narrow width W1 and a relatively large height H. A problem with the production of micro extrusion structures is that the extruded material is necessarily a fluid (i.e., liquid or paste), and as such is subjected to settling after being extruded.
Therefore, the ideal rectangular shape shown in FIG. 12(A) typically settles due to its characteristics as a fluid, as indicated by the arrows shown in FIG. 12(B), causing the idealized high aspect-ratio gridline structure 20B to assume a slumped shape having at least one of a wider width W2 and a reduced height H2. This reduction in height and increase in width is undesirable in, for example, solar cell production where the extruded structure can be used to form metal gridlines because the settled structure allows less sunlight to enter substrate 101, and more sunlight (depicted by dashed-line arrows) is reflected away from substrate 101. Consequently, conventional micro extrusion techniques are limited, for example, in that they cannot render relatively high aspect-ratio (e.g., 1:1 or greater) or porous structures for a cost below $1/sq. ft. Thus, extrusion typically is not used for creating conducting contacts and/or channels for electrochemical (e.g., fuel), solar, and/or other types of cells, which leverage high aspect-ratio fine featured porous structures to increase efficiency and electrical power generation.
Another practical device that benefits from rapid and economical means for generating high aspect ratio lines and features include plasma display panels, such as that shown in FIG. 13, where high aspect-ratio barrier ribs define the sub-pixels within the display. The barrier rib is an electrically insulating structure, and is preferably a high aspect ratio structure, as this improves the dot per inch resolution and fill factor of the display. The settling problem discussed above with reference to FIG. 12(B) results in non-optimal barrier ribs that produce inferior display devices.
What is needed is a system and method for efficiently producing micro extrusion structures that can be used, for example, in the production of high quality photovoltaic cells and plasma display panels.